The transverse flux machine (TFM) topology is an example of a modulated pole machine. It is known to have a number of advantages over conventional machines. The basic design of a single-sided radial flux stator is characterized by a single, simple phase winding parallel to the air gap and with a more or less U-shaped yoke section surrounding the winding and exposing in principal two parallel rows of teeth's facing the air gap. The state-of-art multi-phase arrangement is characterized by stacking magnetically separated single phase units perpendicular to the direction of motion of the rotor or mover. The phases are then electrically and magnetically shifted by 120 degrees for a three-phase arrangement to smooth the operation and produce a more or less even force or torque independent of the position of the rotor or mover. Note here that the angle referred to is given in electrical degrees which is equivalent to mechanical degrees divided by the number of pairs of magnetic poles.
A cylindrical motor uses a concentric stator and rotor, and the motion is then considered as rotational or as an end-less rotation. A linear machine uses translation motion that is normally not a closed motion pattern but may be a back-and-forward motion along a ‘line’. The linear machine or driver has a mover instead of a rotor. The magnetic circuit may be arranged by the same basic magnetic principles in both a rotor and mover, however the geometries will differ.
An example of an efficient rotor or mover arrangement is the use of so called buried magnets combined with soft magnetic pole sections or pieces to allow the permanent magnet field to flux-concentrate or be flexible in a direction transverse to the motion as e.g. described in the patent application WO2007/024184 by Jack et al.
WO2007/024184 discloses an electrical, rotary machine, which includes a first stator core section being substantially circular and including a plurality of teeth, a second stator core section being substantially circular and including a plurality of teeth, a coil arranged between the first and second circular stator core sections, and a rotor including a plurality of permanent magnets. The first stator core section, the second stator core section, the coil and the rotor are encircling a common geometric axis, and the plurality of teeth of the first stator core section and the second stator core section are arranged to protrude towards the rotor. Additionally the teeth of the second stator core section are circumferentially displaced in relation to the teeth of the first stator core section, and the permanent magnets in the rotor are separated in the circumferential direction from each other by axially extending pole sections made from soft magnetic material.
The stacking of the individual stator phase sections is normally based on a physical magnetic separation in-between the individual phase-sections to reduce the magnetic coupling in-between the phases that possibly can have an effect of reducing the effective flux in the air gap during operation.
It is desirable in some applications to provide a machine that is as geometrically compact as possible to fit in a given limited space and to be able to have a high volume specific performance e.g. expressed as Torque per Volume [Nm/m3].
A conventional, balanced 120 degree phase shift, three-phase sinusoidal or trapezoidal drive scheme does not fully engage the core magnetically during the time cycling of operation, and therefore a significant part of the total stator core volume is constantly inefficiently used.
Thus prior art discloses tuning of a set of three phase units at phase orders 0°, 120°, and 240°.
It remains a problem to optimize performance numbers or values, such as torque pr. volume and/or torque pr. current.
EP 1005136 discloses a transverse flux machine having combined phases. However, it remains desirable to provide a simpler construction of such an electrical machine.